Method for transferring variable isochronous data and apparatus therefor

ABSTRACT

A method for transferring variable isochronous data and an apparatus therefor are provided. The method for transferring variable isochronous data includes the steps of (a) determining isochronous transfer to be terminated when the bus is in an idle state for a time interval which is larger than an isochronous gap period, (b) detecting a residual gap having a time interval which is larger than the time interval of an isochronous gap and smaller than the time interval of a subaction gap, (c) checking whether bandwidth for the transfer of isochronous data remains when the residual gap is detected in the step (b), and (d) transferring the isochronous data when it is determined that the bandwidth remains in the step (c). According to the variable isochronous data transfer method, it is possible to maximize the isochronous transfer by selectively using the residual bandwidth, which is assigned for the transfer of the isochronous data but is not used for the real transfer of the isochronous data, for the transfer of the isochronous data.

This is a divisional of application Ser. No. 09/441,955, filed Nov. 17,1999, now U.S. Pat. No. 6,611,886; the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for transferring isochronousdata and an apparatus therefor, and more particularly, to a method fortransferring variable isochronous data using the IEEE 1394 standard.

2. Description of the Related Art

It is possible to transfer data at a high speed by the IEEE 1394 serialbus. It is also possible to perform real time data transfer for amultimedia application by the IEEE 1394 bus. FIG. 1 shows the cycleconfiguration of the IEEE 1394 bus according to a conventionaltechnology. In the IEEE 1394 bus, the maximum bandwidth of anisochronous transfer phase (100 μs) and the minimum bandwidth of anasynchronous transfer phase (25 μs) are specified in the P-1394specification. In general, isochronous transfer is used for real timedata transfer and asynchronous transfer is used for data transfer forvarious commands such as reproduction, rewind, pause, and change ofchannels. Therefore, the maximum bandwidth of an entire isochronouscycle (125 μs) is specified.

FIG. 2 shows the gap timing of the IEEE 1394 bus according to aconventional technology. Referring to FIG. 2, according to the gaptiming of the IEEE 1394 bus, isochronous packets, to which anarbitration bit, a data prefix bit, and a data end bit are added, aretransferred with isochronous gaps interleaved therebetween. At thistime, an acknowledge packet which indicates acknowledge to request canbe transferred after an acknowledge gap.

In order to explain the isochronous transfer of a packet having theabove gap timing, the main steps of a method of assigning isochronousbandwidth in the IEEE 1394 bus according to the conventional technologyare shown in FIG. 3. A node which manages the IEEE 1394 bus can be anisochronous resouce manager (IRM), according to a control situation. Thenode which becomes the IRM includes a bandwidth available (BA) registerwhich manages isochronous resources, in a control and status register(CSR) defined by the IEEE 1394 bus standard. Other nodes in the IEEE1394 bus read the value of the BA register of the IRM in order toperform an isochronous transfer. Then, it is determined whether there isbandwidth to be assigned and the isochronous transfer is performed whenthere is bandwidth to be assigned. At this time, the entire availablebandwidth is generally assigned in a process of assigning the bandwidth.However, the entire assigned bandwidth is not used in a real isochronoustransfer process. Also, in the IEEE 1394 bus, the bandwidth is assigned,assuming that transfer, according to a corresponding application of anode, is in the form of a constant bit rate (CBR) of an asynchronoustransfer mode (ATM). Therefore, when the transfer is in the form of avariable bit rate, residual bandwidth results. For example, applicationsusing the IEC-61833 standard are given much weight in the IEEE 1394applications. In the isochronous transfer method for audio/video devicesaccording to the IEC-61833 standard, it is specified that only a headeris transferred to a corresponding isochronous cycle when there is nodata to be transferred. As a result, in such a case, the entire assignedbandwidth is not used, and there are cases where only necessary data istransferred only when necessary in order to prevent the repeatedtransfer of data and to facilitate the controlling of a buffer. Thus,pertinent, the assigned bandwidth is not used at all.

FIG. 4 shows the relationship between the assignment of bandwidth andthe use of bandwidth in the IEEE 1394 bus according to the conventionaltechnology. Referring to FIG. 4, the horizontal axis shows the degree ofthe use of an isochronous channel and the vertical axis shows bandwidthavailable. Since the assigned bandwidth increases as the use of thechannel increases, free bandwidth is relatively reduced. However, sincethe entire assigned bandwidth is not used during the real isochronoustransfer as mentioned above, residual bandwidth is generated as shown inFIG. 4. Therefore, in the method for transferring the isochronous dataaccording to the conventional technology, the bandwidth is noteffectively used. Also, no more bandwidth can be assigned although thereis bandwidth which can be used after a break point.

It will now be explained how isochronous and asynchronous transfer modessupported in the 1394 bus are distinguished from each other and how thechannels and bandwidth used for the isochronous transfer are managed.Also, the transfer service of the isochronous transfer mode of the 1394bus will be simply compared with the transfer service of theasynchronous transfer mode (ATM).

The 1394 bus provides two transfer modes, namely, an isochronoustransfer mode and an asynchronous transfer mode. In isochronoustransfer, one packet can be transferred every isochronous cycle of 125μs to provide real-time transfer. Meanwhile, in the asynchronoustransfer, which is a transfer mode where data transfer is guaranteed,the data transfer is controlled by a fairness interval where allconnected modes can transfer data only once in the interval. Isochronousand asynchronous data are transferred for one isochronous cycle, whichis started by the cycle start packet transferred from a root node. Theisochronous transfer is prior to the asynchronous transfer. However, inorder to prevent a situation where the asynchronous transfer can not beperformed at all due to the isochronous transfer, only 80% of the entirecycle can be used for the isochronous transfer. Namely, at least 20% ofthe entire cycle can be used for the asynchronous transfer. If theisochronous transfer does not exist, the entire cycle can be used forthe asynchronous transfer.

TABLE 1 Transfer classification Asynchronous Broadcast StreamCharacteristics Isochronous Read/Write write channel Time Yes No No Noguaranteed Arrival No Yes No No guaranteed Broadcast Yes No Yes YesChannel Not specified Not concerned Yes shared

As shown in Table 1, asynchronous read and write, asynchronous broadcastwrite, and asynchronous stream channel which is newly defined in theP1394a specification can be used in the ATM. Here, guaranteed deliveryof data through an identification process can be performed only by theasynchronous read and write.

Channels and bandwidth of the IEEE 1394 bus are respectively assignedusing the values of two registers, CHANNELS_AVAILABLE (CA) andBANDWIDTH_AVAILABLE (BA) of the IRM which are determined after resettingthe bus. The channels and bandwidth must be previously assigned from theIRM to an application wherein isochronous transfer of data is desired tobe performed using asynchronous lock transaction in order to maintainintegrity of resource information. Accordingly, a concerned node cantransfer data of an assigned bandwidth using the assigned channels andbandwidth regardless of whether other nodes use the bus. Namely, it canbe considered as using an additional physical channel having a bandwidthas large as the assigned bandwidth. Since the assignment unit of theisochronous bandwidth is calculated using the time taken to send 1quadlet of 4 bytes in S1600 (1.6 Gbps) specification, the initial valueof the BA register becomes 4915. The value four times the value readfrom the BA must be assigned as a bandwidth assignment value in S400specification. In the case of the asynchronous stream service defined inthe P1394a standard, channels are used like in the isochronous service,however, the bandwidth is not assigned. Therefore, the asynchronousstream service cannot be used for real-time transfer.

The largest difference between the 1394 transfer and the ATM transferlies in the sizes of transfer units. A packet having a variable sizewhere the maximum size of the transfer unit is determined in proportionto transfer speed is used in the 1394 transfer. Meanwhile, a cell havinga fixed size of 53 bytes is used as the transfer unit for high speedprocessing in the ATM transfer. Another difference lies in that atransfer line to which a switch is connected can be controlled in theATM transfer and that the use of the bus by other nodes cannot bedirectly controlled in the 1394 transfer. It is difficult to effectivelyuse the bandwidth, maintaining uniform transfer ability andcharacteristics when the 1394 transfer is used together with the ATMtransfer due to basic differences. Therefore, a method of decreasingsuch differences must be provided. The IEEE 1394 specification issimilar to the Ethernet, which is widely used as a LAN, excluding theisochronous transfer function. The transfer characteristic of the 1394transfer is simply compared with the transfer characteristic of the ATMtransfer in Table 2.

TABLE 2 Transfer classification IEEE 1394 ATM Physical medium Shared(multiple Private/Switching access) (point to point) AddressingOperation node ID Fixed address (IEEE-1212) Data unit Variable lengthpacket Fixed cell (53 bytes) Transfer rate control Non-connectionConnection (VPC and VCC) Fairness Packet size based Cell rate basedbandwidth bandwidth Real time transfer HN, DAN, and CAN LAN, MAN, andWAN

The QOS characteristic of the ATM transfer is shown in Table 3.

TABLE 3 QOS Character- Constant bit Variable bit Available bitUnspecified istics rate (CBR) rate (VBR) rate (ABR) bit rate (UBR) CDV(cell Yes Yes No No delay variable) CTD (cell No Yes No No transferdelay) CLR (cell Yes Yes Yes No loss ratio) Variables for Not PCR andPCR and Non (perform preparing specified SCR MCR optimal effort)bandwidth

As shown in Table 3, there are four services, CBR, VBR, ABR, and UBR inthe ATM transfer service as shown in Table 3. Real-time transfer can beperformed by the services, CBR and VBR among these services.

However, the isochronous transfer of the IEEE 1394 corresponds to theCBR service for processing data having a specific bit rate in view ofthe ATM. The asynchronous transfer, where delivery by the best-effort isassumed, is similar to the UBR service of the ATM, excluding theguaranteed delivery characteristic. For example, the bandwidth of theATM is first assigned to the CBR and VBR services and the remainingbandwidth is assigned to the ABR and UBR services. The ABR service hasthe characteristics of both the VBR and UBR services. As a result,according to the conventional 1394 standard, the VBR and ABR services ofthe ATM are not properly supported.

SUMMARY OF THE INVENTION

To solve the above problem, it is an object of the present invention toprovide a variable isochronous data transfer method for transferringisochronous data using residual bandwidth, which is not used for thetransfer of isochronous data, among assigned channels.

It is another object of the present invention to provide a variableisochronous data transfer apparatus for realizing the above method.

It is another object of the present invention to provide a variableisochronous data transfer method for transferring isochronous data usingresidual bandwidth, which is not used for the transfer of isochronousdata, among assigned channels and supporting a variable bit ratecorresponding to an ABR service.

It is another object of the present invention to provide a variableisochronous data transfer apparatus for realizing the above method.

It is another object of the present invention to provide a variableisochronous data transfer method for transferring isochronous data usingresidual bandwidth, which is not used for the transfer of isochronousdata, among assigned channels, supporting a variable bit ratecorresponding to an ABR service, and performing real time transfer.

It is another object of the present invention to provide a variableisochronous data transfer apparatus for realizing the above method.

Accordingly, to achieve the first object, there is provided a variableisochronous data transfer method for transferring data of apredetermined time interval within a predetermined time on the IEEE 1394bus, comprising a detection step of indicating that there is residualbandwidth, which is not used for the transfer of isochronous data, amongassigned bandwidth, and detecting residual gaps having a predeterminedtime interval and a variable isochronous transfer step of determiningwhether bandwidth for isochronous transfer of data remains when theresidual gap is detected in the detection step and transferring theisochronous data according to determination result. The time interval ofthe residual gap detected in the detection step is larger than anisochronous gap and smaller than a subaction gap.

Also, the variable isochronous transfer step comprises a first detectionstep of detecting an isochronous reset gap and a second determinationstep of determining whether there is enough residual bandwidth in whichto perform the isochronous transfer of data when the isochronous resetgap is detected in the first detection step. Also, the variableisochronous transfer step comprises a step of transferring anisochronous packet when it is determined that there is enough residualbandwidth in the second determination step and a second detection stepof detecting an isochronous reset gap, returning the process to thesecond determination step when the isochronous reset gap is detected,and proceeding the process to an asynchronous phase when the isochronousreset gap is not detected.

Also, the variable isochronous data transfer method according to thepresent invention preferably further includes a first determination stepof determining whether the transfer of data is performed in the currentisochronous reset gap when the isochronous reset gap is detected in thefirst detection step. The second determination step preferably furthercomprises a step of determining whether there is enough residualbandwidth in which to perform the isochronous transfer when it isdetermined that there is no transfer of data in the first determinationstep.

In order to achieve the second object, there is provided a variableisochronous data transfer apparatus according to the present inventionfor transferring data of predetermined bandwidth within a predeterminedtime on the IEEE 1394 bus, including means for indicating that there isresidual bandwidth which is not used for the transfer of the isochronousdata in the assigned bandwidth and for detecting a residual gap having apredetermined time interval, and variable isochronous transfer means fordetermining whether bandwidth for the isochronous transfer of dataremains when the residual gap is detected by the detection means andtransferring the isochronous data according to the determination result.

The residual gap detection means comprises a clock signal generator foroutputting a clock signal of a predetermined period, an idle detectorfor detecting an idle state, a counter for digitizing the clock signalin response to the clock signal output from the clock and digitizing anidle state detection signal output from the idle detector, and a decoderfor determining the time interval of the idle state according to thedigitized value of the counter. Also, the residual gap detection meanscomprises an isochronous gap detector for indicating the start of theisochronous data and detecting an isochronous gap having a predeterminedfirst time interval, a residual gap detector for indicating the start ofthe residual bandwidth and detecting the residual gap having a secondpredetermined time interval which is larger than the first timeinterval, a subaction gap detector for indicating the start of anasynchronous transfer phase and detecting a subaction gap having a thirdpredetermined time interval which is larger than the secondpredetermined time interval, and an arbitration reset gap detector forindicating that arbitration reset is requested and detecting anarbitration reset gap having a fourth predetermined time interval whichis larger than the third predetermined time interval.

Also, when a time interval between the time interval of the isochronousgap and the time interval of the subaction gap is T and an arbitraryinteger larger than 1 is N, the clock signal output from the clocksignal generator has a period of T/N.

In order to achieve the third object of the present invention, there isprovided an isochronous data transfer method realized in a variableisochronous data transfer apparatus including a variable isochronoustransfer buffer (VITF), a constant isochronous transfer buffer (CITF),and an asynchronous transfer buffer (ATF), for isochronouslytransferring data within a predetermined time on the IEEE 1394 bus,comprising the steps of transferring isochronous data through the CITFin an isochronous phase, transferring ABR data through the VITF in avariable isochronous phase, moving the portion corresponding to minimumbandwidth (MBW) in the ABR data output through the VITF from the VITF tothe CITF and transferring the portion corresponding to the MBW throughthe CITF in the isochronous phase, and transferring asynchronous datathrough the ATF in an asynchronous phase.

In order to achieve the fourth object of the present invention, there isprovided an isochronous data transfer apparatus for isochronouslytransferring data within a predetermined time interval on the IEEE 1394bus, comprising a constant isochronous transfer buffer (CITF) forstoring and outputting isochronous data in a first-in first-out (FIFO)manner in order to transfer the isochronous data in an isochronousphase, a variable isochronous transfer buffer (VITF) for storing andoutputting ABR data in the FIFO manner in order to transfer the ABR datain a variable isochronous phase, feed-back means for moving the portioncorresponding to the MBW in the ABR data output through the VITF fromthe VITF to the CITF and transferring the portion corresponding to theMBW through the CITF in the isochronous phase, and an asynchronoustransfer buffer (AFT) for storing and outputting asynchronous data inthe FIFO manner in order to transfer the asynchronous data in anasynchronous phase.

In order to achieve the fifth object of the present invention, there isprovided a variable data transfer method for isochronously transferringdata within a predetermined time on the IEEE 1394 bus, comprising thesteps of (a) determining that isochronous transfer of data is terminatedwhen the bus is in an idle state for a time interval longer than anisochronous gap period and detecting a residual gap having a firstpredetermined time interval which is larger than the time interval ofthe isochronous gap and smaller than the time interval of a subactiongap, (b) determining whether the detected gap is an isochronous resetgap having a second predetermined time interval which is larger than thefirst predetermined time interval and smaller than the time interval ofthe subaction gap, (c) enabling an isochronous arbitration reset bitwhen the detected gap is determined to be the isochronous reset gap inthe determination step, (d) determining whether the isochronous resetbit is enabled when it is determined that the detected gap is not theisochronous reset gap in the determination step and proceeding theprocess to an asynchronous phase, (e) determining whether real-timetransfer packets exist, (f) checking timing when real-time transferpackets exist in the step (e), throwing away the packets which deviatefrom a real-time reference, and transferring the packets which do notdeviate from the real-time reference, (g) determining whether bandwidthis sufficient with respect to packets which are not real-time packetsand packets which are real-time packets and do not deviate from thereal-time reference, and performing arbitration with respect to realtime packets and packets which are not real-time, (h) transferring thepackets when the arbitration is successful, and (i) transiting a phaseto the asynchronous phase.

In order to achieve the sixth object of the present invention, there isprovided an isochronous data transfer apparatus for isochronouslytransferring data within a predetermined time interval on the IEEE 1394bus, comprising means for determining that isochronous transfer of datais terminated when the bus is in an idle state for a time intervallonger than an isochronous gap period and detecting a residual gaphaving a first predetermined time interval which is larger than the timeinterval of the isochronous gap and smaller than the time interval of asubaction gap, means for determining whether the detected gap is anisochronous reset gap having a second predetermined time interval whichis larger than the first predetermined time interval and smaller thanthe time interval of the subaction gap, means for enabling anisochronous arbitration reset bit when the detected gap is determined tobe the isochronous reset gap by the detection means, means fordetermining whether the isochronous reset bit is enabled when it isdetermined that the detected gap is not the isochronous reset gap by thedetermination means and driving an asynchronous transfer mode when theisochronous reset bit is not enabled, means for determining whetherreal-time transfer packets exist, means for checking timing whenreal-time transfer packets exist, throwing away the packets whichdeviate from a real-time reference, and transferring the packets whichdo not deviate from the real-time reference, means for determiningwhether bandwidth is sufficient with respect to packets which are notreal-time packets and packets which are real-time packets and do notdeviate from the real-time reference, means for transferring the packetswhen the arbitration is successful, and means for performingasynchronous transfer of data.

BRIEF DESCRIPTION OF THE DRAWING(S)

The above objects and advantages of the present invention will becomemore apparent by describing in detail a preferred embodiment thereofwith reference to the attached drawings in which:

FIG. 1 shows the cycle configuration of the IEEE 1394 bus according to aconventional technology;

FIG. 2 shows the gap timing of the IEEE 1394 bus according to theconventional technology;

FIG. 3 is a flowchart for describing a method of assigning isochronousbandwidth in the IEEE 1394 bus according to the conventional technology;

FIG. 4 shows a relationship between the assignment of bandwidth and theuse of bandwidth in the IEEE 1394 bus according to the conventionaltechnology;

FIG. 5 is a flowchart for showing the main steps of a variableisochronous transfer method according to an embodiment of the presentinvention;

FIG. 6 shows the gap timing of the IEEE 1394 bus for describing thevariable isochronous transfer method according to the embodiment of thepresent invention;

FIG. 7 is a block diagram for showing the structure of hardware fordetecting a residual gap in the variable isochronous transfer methodaccording to the present invention;

FIG. 8 shows processes of detecting the residual gap in the variableisochronous transfer method according to the present invention;

FIG. 9 shows the cycle configuration of the IEEE 1394 bus in thevariable isochronous transfer method according to the present invention;

FIG. 10 shows the relationship between the assignment of bandwidth andthe use of bandwidth in the IEEE 1394 bus in the variable isochronoustransfer method according to the present invention;

FIG. 11 describes the control of the flow of an ABR service applied tothe variable isochronous transfer method according to the embodiment ofthe present invention;

FIG. 12 shows the structure of bandwidth in a variable isochronoustransfer method according to another embodiment of the presentinvention;

FIG. 13 shows the structure of a buffer for realizing the ABR-1394 datatransfer as the variable isochronous data transfer method according toanother embodiment of the present invention;

FIG. 14 shows an example of processes of transferring data by thevariable isochronous data transfer method according to anotherembodiment of the present invention; and

FIG. 15 is a block diagram for showing the main steps of the variableisochronous transfer method according to another embodiment of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 5 is a flowchart for showing the main steps of a variableisochronous transfer method according to an embodiment of the presentinvention. Referring to FIG. 5, the variable isochronous data transfermethod according to the present invention includes a step 502 ofdetecting a residual gap and a variable isochronous transfer step 52.

In the residual gap detection step 502, the residual gap is detected bychecking a time interval which maintains an idle state. Namely, theresidual gap has a predetermined time interval, which is distinguishedfrom other gaps, and indicates that there is residual bandwidth which isnot used for the transfer of isochronous data in assigned bandwidth.Although not shown, when the bus is in an idle state for a time longerthan an isochronous gap period in a normal isochronous transfer step500, the residual gap is detected by performing a step (not shown) ofdetermining that the isochronous transfer is terminated and checking thetime interval which maintains the idle state.

The variable isochronous transfer step 52 includes a first detectionstep 524, first and second determination steps 526 and 528, anisochronous packet transfer step 530, and a second detection step 532.An isochronous reset gap is detected in the first detection step 524.The isochronous reset gap for setting an isochronous fairness intervalhas a time interval larger than the residual gap and smaller than thesubaction gap. Namely, since there is high possibility that a node closeto the root node occupies the bus, in the IEEE 1393 bus, the isochronousfairness interval is set in order to let a node perform the isochronoustransfer only once in the interval. When the isochronous reset gap isdetected in the first detection step, it is then determined whether thetransfer of data is performed in the current isochronous reset gap inthe first determination step 526. When it is determined that thetransfer of data is not performed in the first determination step, it isdetermined whether there is enough residual bandwidth in which toperform the isochronous transfer in the second determination step 528.When it is determined that there is enough residual bandwidth in thesecond determination step, an isochronous packet is transferred (530).In the second detection step 532, the isochronous reset gap is detected,the process returns to the second determination step when theisochronous reset gap is detected, and the process proceeds to anasynchronous phase when the isochronous reset gap is not detected.Therefore, when the isochronous reset gap is detected, the transfer ofthe isochronous data is performed. When the isochronous reset gap is notdetected, it is checked whether the transfer of the isochronous data isperformed in the isochronous reset gap and the transfer of theisochronous data is performed. Fairness is achieved in the transfer ofisochronous data among a plurality of nodes.

The respective steps of the variable isochronous transfer methodaccording to the present invention can be realized by inputtingappropriate program codes to a physical (PHY) chip as understood bythose skilled in the art. Also, the above-mentioned variable isochronoustransfer method according to the present invention can be made a programwhich can be executed by computers and can be realized by generalpurpose digital computers which operate the program from computerreadable media. The media include magnetic recording media such asfloppy disks and hard disks, optical recording media such as CD-ROMs andDVDs, and storing media such as carrier wave and transmission throughthe Internet. Also, such functional programs, codes, and code segmentscan be easily estimated by programmers in the technical field to whichthe present invention belongs.

FIG. 6 shows the gap timing of the IEEE 1394 bus for describing avariable isochronous transfer method according to an embodiment of thepresent invention. Referring to FIG. 6, the gap timing of the IEEE 1394bus according to the variable isochronous transfer method of theembodiment of the present invention is divided into a normal isochronousphase, a variable isochronous phase, and an asynchronous phase. Twoisochronous packets are transferred in the normal isochronous phase. Thevariable isochronous phase starts by detecting the residual gap. Theisochronous packets are transferred when the conditions described withreference to FIG. 5 are satisfied. The isochronous reset gap,transmitted by, for example, another node (not shown), is detected and aconcerned isochronous packet is transferred through the bus. Thevariable isochronous phase is terminated by detecting the subaction gapand an asynchronous packet is transferred through the bus by startingthe asynchronous phase. An acknowledge packet is transferred through thebus by another node which receives the asynchronous packet.

FIG. 7 is a block diagram for showing the structure of hardware fordetecting the residual gap in the gap timing described in FIG. 6.Referring to FIG. 7, residual gap detection means includes a clocksignal generator 702, an idle detector 704, a counter 706, a decoder708, and a gap detector 710.

The clock signal generator 702 outputs a clock signal of a predeterminedperiod. The idle detector 704 detects an idle state and outputs an idlestate detection signal. The counter 706 digitizes the time interval ofthe clock signal in response to the idle state detection signal. Thedecoder 708 determines which kind of gap is detected by determining thetime interval of the idle state according to the digitized value of thecounter. The gap detector 710 detects a concerned gap according to thedetermination value output from the decoder 708.

The gap detector 710 preferably includes an isochronous gap detector712, a residual gap detector 714, a subaction gap detector 716, and anarbitration reset gap detector 718. The isochronous gap detector 712detects an isochronous gap which indicates the start of the isochronousdata and which has a first predetermined time interval. The isochronousgap has a time interval of 40 through 50 nsec in the case of the IEEE1394 standard. The time interval of the isochronous gap is set to be thesame as the time interval of the acknowledge gap. The residual gapdetector 714 detects a residual gap which indicates the start of theresidual bandwidth and which has a second predetermined time intervalwhich is larger than the first predetermined time interval. Thesubaction gap detector 716 detects a subaction gap which indicates thestart of the asynchronous transfer phase and which has a thirdpredetermined time interval which is larger than the secondpredetermined time interval. Finally, the arbitration reset gap detector718 detects an arbitration reset gap which indicates that arbitrationreset is requested and which has a fourth predetermined time intervalwhich is larger than the third predetermined time interval. As mentionedabove, the variable isochronous data transfer apparatus including thegap detection means according to the embodiment of the present inventiondetects a residual gap which indicates the start of the residualbandwidth and which has a second predetermined time interval which islarger than the first predetermined time interval by including theresidual gap detector 714 in the gap detector for determining the kindof gap according to the time interval of the gap.

FIG. 8 shows processes of detecting the residual gap in the variableisochronous transfer method according to the present invention. When theidle state is detected in a non-idle state 800, an idle state timer suchas the counter 706 described with reference to FIG. 7 is reset and thenon-idle state 800 is transited to an isochronous gap state 802. If theidle state is terminated in the first predetermined time interval andthe time interval of the concerned gap measured by the idle state timeris determined to be within the first predetermined time, the isochronousgap is detected and the isochronous gap state 802 is transited to thenon-idle state 800. When the time interval of the concerned gap exceedsthe first predetermined time interval, it is determined that theconcerned gap is not the isochronous gap and the isochronous gap state802 is transited to a residual gap state 804 for determining whether theconcerned gap is the residual gap. When the time interval of theconcerned gap exceeds the second predetermined time interval, theresidual gap state 804 is transited to the subaction gap state 806. Whenthe time interval of the concerned gap exceeds the third predeterminedtime interval, the subaction gap state 806 is transited to anarbitration reset gap state 808. Accordingly, gaps having differentpredetermined time intervals can be detected in the order of the size ofthe time interval.

FIG. 9 shows the cycle configuration of the IEEE 1394 bus in thevariable isochronous transfer method according to the present invention.Referring to FIG. 9, in the isochronous transfer method according to theconventional technology, the entire assigned bandwidth is considered tobe used and notations of residual bandwidth do not exist in the cycleconfiguration of the IEEE 1394 bus. However, it is possible to detectthe residual bandwidth and to transfer isochronous data selectivelyusing the residual bandwidth in the cycle configuration of the IEEE 1394bus according to the variable isochronous transfer method of the presentinvention.

FIG. 10 shows the relationship between the assignment of bandwidth andthe use of bandwidth in the IEEE 1394 bus in the variable isochronoustransfer method according to the present invention. Referring to FIG.10, even in the case of a break point, namely, the point from which nomore isochronous resources can be assigned, it is possible to performthe isochronous transfer using the variable isochronous phase by theresidual bandwidth.

A new ABR data transfer method for 1394 (ABR-1394) which is similar tothe ABR service of the ATM will be explained as a method for utilizingremaining bandwidth recognized by the above-mentioned variableisochronous data transfer method. Some multimedia data having a variablebit rate can be effectively transferred using the ABR-1394 service. Inorder to provide a technical understanding, the ABR service of the ATMwill be described.

There are applications where bandwidth to be used cannot be correctlypredicted among the applications. In these cases, the ABR service of theATM (an ABR-ATM service) is used. The ABR service is applied to thevariable isochronous transfer method according to the embodiment of thepresent invention.

FIG. 11 is a view for explaining the control of the flow of the ABRservice. Referring to FIG. 11, an additional closed end-to-end controlloop is formed in order to control the flow of the transferred data inthe ABR-ATM service. A resource management (RM) cell for checkingnetwork traffic is transferred through the control loop. Trafficinformation is recorded in the RM cell and the RM cell passes throughnetwork elements and returns to a source. One RM cell is transferred toeach of N data cells. Here, a congestion-marking bit is included in thesimplest method for recording information in the RM cell in order tocontrol the transfer rate of the source. An explicit cell rate isindicated in a more developed method. If the RM cell is not returned tothe source, congestion is assumed and the source automatically reducesthe transfer rate. The ABR-ATM service where bandwidth left after beingassigned to the CBR and VBR services is used is used for applicationshaving high resilience such as file transfer and mail on protocols suchas TCP/IP, IPX/SPX, and APPN.

Also, a method of utilizing the discriminated remaining bandwidth in theapplications must be provided. What matters is how to provide themethod. The VBR and ABR services are not directly supported in the IEEE1394 standard among the transfer modes of the ATM. However, since theVBR service has significantly more complicated transfer parameters andconnection admission control mechanism, it is difficult to directlysupport the VBR service in the IEEE 1394 standard which realizes adistribution protocol. Therefore, a transfer service corresponding tothe ABR service of the ATM which has a common point of using theremaining bandwidth with the VBR service is realized. The ABR-ATM is notsuitable for the transfer of multimedia data since real time transfer isnot assumed in the ABR-ATM. However, the ABR-1394 to be provided can beused for the transfer of multimedia data since real-time transfer usingthe isochronous bandwidth can be performed in the ABR-1394. Hereinafter,a variable isochronous transfer method according to another embodimentof the present invention, which is called ABR-1394 will be described.

FIG. 12 shows the structure of the bandwidth in the variable isochronoustransfer method according to another embodiment of the presentinvention. Referring to FIG. 12, minimum bandwidth (MBW) and peakbandwidth (PBW), which must be satisfied, are specified like in theABR-ATM in applications where variable bit rate data are to betransferred using the ABR-1394. Since the MBW must be satisfied, the MBWis processed using normal isochronous bandwidth assignment and transfermethods. Variable bandwidth (VBW) obtained by subtracting the MBW fromthe PBW is processed in a variable isochronous phase (VIP) since whetherto transfer the isochronous data is determined according to the load onthe current bus in the VBW. Since it is difficult to dynamically changethe size of the packet of the IEEE 1394, which decide on the bandwidth,after once the size of the packet is determined, the VBW is set to amultiple of the MBW. If the VBW is not a multiple of the MBW, a multipleof PBW included in the VBW is assigned as the bandwidth. Downsizing of aPBW than the PBW specified by a user is performed so that the capacityof a buffer maintained in the application is not exceeded. Also,connection admission is performed only by the MBW in the ABR-1394.Namely, if the isochronous bandwidth can be assigned by the MBW, it ispossible to use the concerned ABR-1394 service.

A variable isochronous data transfer method according to anotherembodiment of the present invention will now be described. The variableisochronous data transfer method is for realizing the ABR-1394 servicewhich is defined above. The core of the variable isochronous datatransfer method is a method of constituting and managing the buffer.According to the variable isochronous data transfer method according tothis embodiment of the present invention, the packet of the variablebandwidth left after being transferred in a normal constant isochronoustransfer phase (CIP), is transferred in the variable isochronoustransfer phase (VIP) bandwidth assigned as the MBW in the ABR-1394. Atthis time, the packet left in the VIP is transferred within a rangeallowed by the PBW and the remaining bandwidth. It is necessary toseparate a conventional isochronous transmission FIFO (ITF) into twobuffers, namely, a constant isochronous transfer buffer (CITF) and avariable isochronous transfer buffer (VITF). This is because normalisochronous packet transfer may be prevented by the variable bandwidthof the ABR where it is not possible to correctly predict how manypackets can be transferred when the conventional ITF is used withoutbeing separated. FIG. 13 shows the structure of a buffer for thetransfer of the ABR-1394 data. Referring to FIG. 13, the partcorresponding to the MBW is moved from the VITF to the CITF and istransferred since the MBW in the ABR data must be guaranteed to betransferred through the separated VITF. The part corresponding to theMBW cannot be moved to the CITF from the beginning because the transferorder of the packets must be maintained, that is, the packets left afterbeing transferred in a previous VIP must be transferred in the CIP.Separate buffers must be used for the respective ABR service requests inthe case of the VITF. Meanwhile, a common CITF is used for allisochronous requests. This is because it is not possible to predict thesize of the VBW included in each ABR request, namely, the number ofpackets, in the respective cycles.

FIG. 14 shows an example of processes of transferring data by a variableisochronous data transfer method according to another embodiment of thepresent invention. Referring to FIG. 14, the processes of transferringdata by the variable isochronous data transfer method according to thisembodiment of the present invention corresponds to the example of thedata transfer performed in an arbitrary bit rate (ABR) node in which theseparate buffers of FIG. 13 are used. When the ABR-1394 packets includedin the variable bandwidth cannot be accepted in the remaining bandwidthcalculated by an internal clock signal generator, the ABR-1394 packetsare transferred in the next cycle. No more than (N−2) packets aretransferred as described with reference to FIG. 12 since the datatransfer having a bandwidth more than the PBW, must not be performedeven if the amount of remaining bandwidth is more than the variablebandwidth.

Since the isochronous stream packets transferred in the VIP aretransferred with no bandwidth assigned, when large load is applied tothe bus, a shortage of bandwidth where data corresponding to thevariable bandwidth cannot be transferred at all by other nodes excludingthe nodes having large node IDs, may occur. This is caused by thearbitration mechanism of the IEEE 1394 bus based on the node IDs. Inorder to solve this problem, fairness with respect to the use of theremaining bandwidth is provided using fairness interval notations usedfor the asynchronous transfer. In order to realize the fairness, amethod of recording the start of the fairness interval and the use ofthe fairness interval with respect to the isochronous transfer of datamust be provided, like in the asynchronous transfer. For this, a newgap, which is larger than the residual gap defined above and smallerthan the subaction gap used in the asynchronous phase, and an enable bitare necessary. The new gap is called an isochronous reset gap and thenew bit is called an isochronous arbitration enable bit. Therefore, theVIP of FIG. 11 can start by the residual gap or the isochronous transferreset gap like the asynchronous phase. Between the sizes of the gapsnewly defined in the present invention and the conventional gap, therelationship, acknowledge gap=isochronous gap<residual gap<subaction gapis concluded. The ABR-1394 service can be used with two options,real-time (RT) and non real-time (NRT).

FIG. 15 shows the main steps of a variable isochronous transfer methodaccording to another embodiment of the present invention. Processes oftransferring isochronous packets in the variable bandwidth including thereal-time option are shown with reference to FIG. 15. When the residualgap is detected, a phase is transited to the variable isochronous phaseand it is determined whether the detected gap is the isochronous resetgap. When the detected gap is determined to be the isochronous resetgap, an isochronous arbitration reset bit is enabled. When the detectedgap is determined not to be the isochronous reset gap, it is determinedwhether the isochronous reset bit is enabled. When the isochronous resetbit is not enabled, the process proceeds to the asynchronous phase. Itis determined whether real-time packets exist. When real-time packetsexist, a step of checking the timing of the packets is performed. Whenthere are packets which deviate from a real-time reference, the packetsare thrown away. A step for performing the transfer of the packets isperformed on the packets which do not deviate from the real-timereference. It is determined whether the bandwidth is sufficient withrespect to packets which are not real-time packets and packets which donot deviate from the real-time reference, and arbitration is performedon the above packets. When the arbitration has successfully performed,the packets have been transferred, the isochronous arbitration reset bithas been disabled, and a transfer channel has been changed to anarbitrary bit rate (ABR) channel, a phase is transited to theasynchronous phase. Therefore, if the real-time option is not used, thetiming is not checked and the packets are not thrown away.

As mentioned above, additional flow control using the RM cell must beperformed in order to maintain the minimum cell rate (MCR) and toutilize the remaining bandwidth in the ABR-ATM. However, additional flowcontrol is not necessary in the variable isochronous data transfermethod according to another embodiment of the present invention(ABR-1394) since the MBW is guaranteed by normal isochronous transfer,the remaining bandwidth is automatically recognized, and the use of theremaining bandwidth is maximized. Namely, the ABR-1394 application candirectly control the transfer rate according to the state of the bus. Acell loss ratio (CLR) is specified in the ABR-ATM and an ATM switchmaintains the CLR. However, in the ABR-1394, the loss ratio with respectto the packets included in the variable bandwidth is not controlled. TheABR-1394 maintains fairness with respect to the use of the remainingisochronous bandwidth in the same way as the ABR-ATM which maintainsfairness with respect to the use of the remaining bandwidth. TheABR-1394 allows restricted isochronous bandwidth to be effectively usedand relatively reduces the size of a unit channel using the MBW, thusallowing more isochronous channels to be simultaneously used. Thecharacteristics of the ABR-ATM are simply compared with thecharacteristics of the ABR-1394 in Table 4.

TABLE 4 Transfer service classification ABR-ATM ABR-1394 Input variablesPCR, MCR, and CLR PBW and MBW Guaranteed bandwidth MCR MBW Usedbandwidth Remaining bandwidth Remaining bandwidth of of assigned CBR andassigned isochronous VBR bandwidth and minimum asynchronous bandwidthTransfer rate control Use RM cells Self control Fairness Non-usedbandwidth Non-used isochronous bandwidth Real-time transfer UnapplicableSupported by real-time (RT) option

Also, the real-time (RT) ABR-1394 service has an advantage of providingimproved quality by receiving additional data, while maintainingcompatibility with the 1394-1995 standard.

Since the residual gap, the isochronous reset gap, and the isochronousreset bit are defined in order to support the bandwidth stealing and theABR-1394 service, it is necessary to modify a physical layer, namely,the PHY chip for the residual gap, the isochronous reset gap, and theisochronous reset bit. Also, it is necessary to modify a link layersince the remaining isochronous remaining bandwidth within 100 μs mustbe able to be calculated using a clock counter of the node. Finally, itis necessary to modify the structure of a new VITF provided for theABR-1394 service and a DMA engine for controlling the VITF.

As mentioned above, an isochronous data transfer method by the bandwidthstealing technique for discriminating the remaining isochronousbandwidth which is not used in the IEEE-1394 bus is provided in thepresent invention. Also, the ABR transfer service for 1394 (ABR-1394)which is similar to the ABR service of the ATM (ABR-ATM), by which it ispossible to effectively transfer multimedia data in the form of VBR, isprovided on the basis of the isochronous data transfer method.

As mentioned above, according to the variable isochronous data transfermethod of the present invention, it is possible to maximize theisochronous transfer by selectively using the residual bandwidth, whichis assigned for the transfer of the isochronous data but is not used forthe real transfer of the isochronous data, for the transfer of theisochronous data.

Also, a chance of transferring multimedia data in the form of the VBR isprovided to the 1394 isochronous transfer where only multimedia data inthe form of the CBR is assumed. Also, the ABR-1394 transfer service,based on the provided technique corresponding to the ABR service whichis useful in the ATM, is simpler and more effective than the ABR-ATMsince the real-time transfer function is additionally provided and it isnot necessary to perform additional flow control.

1. An isochronous data transfer method realized in a variableisochronous data transfer apparatus including a variable isochronoustransfer buffer (VITF), a constant isochronous transfer buffer (CITF),and an asynchronous transfer buffer (ATF), for isochronouslytransferring data within a predetermined time on an IEEE 1394 bus,comprising the steps of: transferring isochronous data through the CITFin an isochronous phase; transferring Available Bit Rate (ABR) datathrough the VITF in a variable isochronous phase; moving a portioncorresponding to minimum bandwidth (MBW) in the ABR data output throughthe VITF and from the VITF to the CITF; and transferring the portioncorresponding to the MBW through the CITF in the isochronous phase; andtransferring asynchronous data through the ATF in an asynchronous phase.2. The method of claim 1, wherein the MBW and peak bandwidth (PBW) arespecified in an application where variable bit rate data is desired tobe transferred using the variable isochronous data transfer method. 3.The method of claim 2, wherein variable bandwidth (VBW) obtained bysubtracting the MBW from the PBW is constituted of the multiples of theMBW in the application.
 4. The method of claim 2, wherein the multiplesof the MBW included in the VBW are assigned as the bandwidth when theVBW is not constituted of the multiples of the MBW in the application.5. The method of claim 1, wherein, when packets included in the VBWcannot be accepted in the remaining bandwidth calculated by an internalclock signal generator, the packets are transferred in the next cycle.6. An isochronous data transfer apparatus for isochronously transferringdata within a predetermined time interval on an IEEE 1394 bus,comprising: a constant isochronous transfer buffer (CITF) for storingand outputting isochronous data in a first-in first-out (FIFO) manner inorder to transfer the isochronous data in an isochronous phase; avariable isochronous transfer buffer (VITF) for storing and outputtingAvailable Bit Rate (ABR) data in the FIFO manner in order to transferthe ABR data in a variable isochronous phase; feed-back means for movinga portion corresponding to the minimum bandwidth (MBW) in the ABR dataoutput through the VITF and from the VITF to the CITF; and transferringmeans for transferring the portion corresponding to the MBW through theCITF in the isochronous phase; and an asynchronous transfer buffer (AFT)for storing and outputting asynchronous data in the FIFO manner in orderto transfer the asynchronous data in an asynchronous phase.